In the image processing technology, specifically, a technology for reducing random noise contained in an image is essential to sharp reproduction of a captured image. A typical technology for reducing random noise is disclosed, for example, in Patent Literature 1.
Patent Literature 1 discloses the following technology. That is, an apparatus includes a plurality of arithmetic circuits for calculating a moving average pixel number (n) based on a specified mathematical formula with respect to an arbitrary target pixel (i) in a main scanning direction of a color digital signal output from an input image processing circuit, a plurality of bit selector circuits for selectively outputting the target pixel (i) and reference pixels (j) preceding and following (n) pixels, a plurality of difference circuits for calculating absolute values of the differences between an output level of the target pixel (i) and an output level of each of the reference pixels (j), a plurality of judging circuits for outputting the target pixel (i), comparing the values output from the plurality of difference circuits with a specified threshold in a threshold memory, to output the reference pixels (j) based on the comparison result, and a plurality of arithmetic circuits for performing the moving average processing of output signals from the plurality of judging circuits.
More specifically, only in a case where an absolute value of the difference between the output level of the target pixel (i) and the output level of the reference pixel (j) is equal to or less than the threshold, the reference pixel (j) is added to the moving average processing. As a result, a portion where the absolute value of the difference varies sharply over the threshold is excluded from the moving average processing. This ensures effective removal of noise components.